1. Field of the Invention
The present invention relates to a reader/writer for a portable recording medium such as an IC card, in particular, to a reader/writer for a portable recording medium which is capable of preventing welding of the power supply unit or breakdown of the device, even when an excess current flows in the power supply unit of the IC card due to short-circuiting failure or the like.
2. Description of the Prior Art
A portable recording medium such as an IC card is constructed by embedding an IC card chip such as memory or microcomputer in a plastic card of credit card size. An IC card has a large memory capacity and is equipped with a control unit such as microcomputer, so that it is suited for memorizing various information, data, and others that require a large memory capacity. Moreover, since its size is adequate for carrying, the device may be considered for various uses such as shopping card and medical examination card, with some of these ideas being put to practical use already.
An IC card is formed with a plurality of terminals exposed on its exterior surface. When an IC card is inserted to a read and write device (referred to as card reader/writer hereafter), the contacts provided in the contact section of the card reader/writer and the corresponding terminals of the IC card are brought to an electrical contact, establishing a supply of operating power from the card reader/writer as well as carrying out the transfer of the data.
However, when something with size of a card is inserted to it, the prior reader/writer transports it, whatever it may be, to the contact section in the interior, causes the contacts in the contact section to be brought to a contact with the inserted body, and carries out supply of power and transfer of data. Because of this, a foreign body like an iron plate is inserted to it, it may lead to the welding of the contacts or to the damages to the card reader/writer due to short-circuiting between the contacts or between the terminals. In order to prevent such a thing from happening, there have been developed card readers/writers that can disconnect the power source, by providing an excess current preventive circuit in them. In such a device, however, the value of the excess current to be detected is generally set at somewhat higher value, so that it is insufficient for preventing the welding of the contacts or the like.